Probabilistic Seismic Assessment of Multiframe Concrete Box-Girder Bridges with Unequal-Height Piers

Abstract

Most long bridges have joints to accommodate thermal expansion and contraction without inducing large forces in the bridge. However, these joints have caused some adverse conditions during earthquakes. In addition, irregular topographical surfaces, creating substructures with pier heights of different lengths, can worsen the seismic vulnerability. This paper examines the seismic behavior of a multiframe concrete box-girder viaduct with four levels of altitudinal irregularity, ranging from regular to highly irregular, using fragility curves. To extend the results for all bridges in the same class, uncertainty related to the earthquake, structural geometries, and materials are considered. Full nonlinear time-history analyses are performed on the three-dimensional analytical finite-element models of the bridge. The results clearly indicate that the bridge fragility increases with the degree of the altitudinal irregularity. In addition, the component fragility parameters show that unseating of the deck at the in-span hinge location is the most vulnerable component.